Hi,
1. The backfocus of the camera is 17mm, with the EFW2 an no difference what filters used the total distance should be around 24/25mm..
2. The cam has a whip mechanical shutter which works really nice!
3. Yep I had one of the first units and it had problems with the shutter, ATIK professionally exchanged my cam instantly and from there on everything worked just like a dream!
In the end the camera is a masterpiece of equipment and I can just recommend it!